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Dreaded Dendrites

I recently acquired a Hammond H100 in very nice condition, but it did have a few problems.

1) The percussion didnít work.
2) The brush didnít seem to work on all keys.
3) The harp sustain seems only too operate on around halve the keys.

There seemed to be a connection here, but there were no common circuitry.

So I started with the percussion and it soon became clear that the problem was not in the percussion amplifier, but in the keyboard. On the H100 the percussion is triggered from a separate set of switches in the keyboard. When I measured the resistance to earth at the output of keyboard, I found that I had a resistance of around 12K, when there should no circuit to earth. I had an earth fault, but how?

I made the decision that the keyboards must come out, thereís no other way. Removing the keyboards on a Hammond is no easy job and not for the faint hearted. Iím no Hammond technician, but I have worked in electronics all of my working life.

After extracting both keyboards and removing the covers on the bench. I started to examine the switch contacts and bus bars. All seemed to look fine, at first, until I noticed a fur like growth over the zinc platted steel panels between the switch leaves. Yes, it was dreaded Dendrites, which explained everything. With an eyepiece I could see whiskers running between the contacts and metal frame. Well, I found the problem, but Iím still not sure how I can get the stuff out without any damage.

Hi Ken, I have the same problem with my E-182. It'll take a zappin only to return in a little while. I wondered if a magnet would attract their furry butts. WD-40, friend or foe? Dendrites seem to live an elusive mysterious life. Congrats on getting your keyboards open. If the H is anything like an E you'll find that your drum machine etc. can be plugged into the old brush input to the power amp. Kinda the way to go. Harp sustain is a tough one. Mine has one clunker key that pops. Looks like a research project. I'm interested in peoples thoughts on the dendrite remedy. I'd also like to know the basic skinny of opening up the keyboard to get at em.

My favorite is descending grades of steel wool, when I can get into the area that needs cleaning that is. I'd start with 00 and do 000 and finish with 0000. I once tried going right to the 0000 and it took forever that way.

Dendrites are fern-like growths which require moisture to create and stay close to the base metal. Whiskers stick up like, well, whiskers. You have described whiskers.

Anyhow, the 'accepted' solution is to simply burn away troublesome whiskers by making a short circuit with the whiskers across a pair of 9V batteries. I've never had to do this, mind you. Knock on wood!

A great (but very time-consuming) solution would be to completely disassemble every affected part, clean it, and paint it when possible. Paint will slow the growth of future whiskers.

I am really impressed...getting the manuals out of an H was no easy task. Replacing them will be a real test of your resolve.

Personally, I would not use any steel wool anywhere on the inside of the keyboard...steel wool tends to shed little bits of (very conductive) steel dust, and you will be worse off if that stuff gets in there.

The whiskers only form on zinc plated surfaces, so those are the only places you need to work on.
The whiskers are really rather fragile, and come off easily. Not sure what the poster above was referring to as far as having to scrub with steel wool. The whiskers come off with a swipe of a finger. On big places like amp chassis, a couple swipes with 0000 steel wool removes every trace of the whiskers. Inside scanners all I use is solvent and a china bristle brush.

I would get some plastic safe contact cleaner like CRC-QD and go in there with small brushes, pipe cleaners, or whatever works, and flush the loose whiskers out with the QD. The force of the QD may be enough to get rid of the whiskers in tight places. If you have access to compressed air, that can help get all residual bits out as well.

I would like to first thank Bobmann. Without your videos I'm not sure if I would have tackled the job. Its true getting the keyboards out was a challenge. I found it was simpler to take both keyboards out together. Plus my H100 was built around 1969 and I think the fixing for the keyboards are different. I found two sets of very long bolts that hold the back sub frame of the keyboards, two above the PSU and two above the amplifier. The plan is to put both keyboards back in together. They are rather heavy, so it’s a two man job.

Since my posting I have now removed the all of the offending Dendrites. By two methods, my first was to simply blowing them out with an Air Duster, you could us air line if you have one, but how do you stop them from coming back. I have seen these blighters in old radio chassis and have found if you cover the effected area with thin oil, keeping the atmosphere out, it seem to stop them from re-growing. Well, instead of using thin oil I used switch cleaner (Servisol). This is a solvent base cleaner, plus a contact lube. The lube is an oil base that will stay is place after the solvent has evaporated. I'm not suggesting you just blast it with switch cleaner, which would end up washing it all over switch wafers. My approach was to us a thin lolly pop stick rapped in thin layer of Ja-cloth, stuck on with Supper Glue. If you saturate the stick with switch cleaner and very carefully slide it down between the switch wafers and wipe the Dendrite off. Keep washing the Denrites off the stick. I think this could well be a complete fix, but time will be the test.

Just as a follow up on my last posting. I have how finished the work on my H100 and all is working fine. It looks like a complete success in removing the Dendrites from the keyboards.

I have included a few photos so you know what these dreaded Dendrites look like. Also in reply to Bobmann’s comments, you were right, getting the keyboards back into H100 did very much test my resolve, many thanks to all of your comments.

One could call this an enlightening experience; I would say it was no walk in the park.

Congraultations on your repair.
Great photos. Some Hammonds have dendrites, most don't. Mine don't. Some of us theorize that organs oiled sometime in their life with oil containing zinc or aluminum could cause this. Most automotive and machine shop oils contain this additive as a rust inhibitor.
I have one H112 with 1980's capacitors on the harp board, one H182 with all original electrolytic capacitors on the harp board. I like the sustain time on the original board, but it is not consistent, the way electrolytics age. 15 uf 10% 25 v electrolytics are about $6 apiece, so I have been thinking of paralleling three 2.2 uf ceramic caps to replace the 110 of these.
The sustain on the organ with the new caps is too long.
My percussion didn't work at all on #9574 until I replaced electrolytic capacitors in the power supply, the power amp, and finally the percussion chassis. Then it worked fine.
If I go into the keyboard that deeply, it will include adding wire to the brush and another contact to bring them out to a velocity encoding midi encloder. On the lower manual, preferably. I realize the lower doesn't have the harp. I'm thinking DC can be added to a sub-fundamental contact, then blocked out of the pickups with capacitance. Midi encoders run off DC.

Thanks for your comments. Yes, it a real puzzle why some organs seem to be plagued with Dendrite growth and others not.

To be precise my H100 is a H112 built around 1969. I bought it around two months ago and most of that time it has been in pieces. Having it all back together and now running into a Leslie760 it sound very nice, but it doesn’t sound like most Hammonds. It’s almost like I’m missing something. I know the percussion is different on the H100, could that have something to do with it? I would be interested to hear your view. When comparing your H112 with other Hammonds does it have that Hammond sound?